As shown in FIG. 1, the human wrist consists of a cluster of 8 small bones, the carpal bones, which flexibly connect the metacarpal bones (15, 16, 17, 18, 19), located in the palm, with the ulna (3) and radius (4) located in the forearm. The carpal bones are generally arranged into distal and proximal rows (5,6). The distal row of carpal bones consists of the trapezium (7), trapezoid (8), capitate (9) and hamate (10) bones. The proximal row of carpal bones consists of the scaphoid (11), lunate (12), triquetrum (13), and pisiform (14) bones. In normal operation of a healthy wrist, the articular surface of the radius (15) provides a concave bearing surface which supports the articulation of the scaphoid (11) and lunate (12) as the wrist goes through its range of motion.
Due to injury, degenerative changes, disease (such as arthritis) or other conditions, a person may experience pain, discomfort, or difficulty when operating the wrist through its range of motion. Known procedures for such wrist conditions are to fuse the scaphoid (11) and lunate (12) bones (and possibly other carpal bones) to themselves in a “four corner” fusion, or, in more extreme cases, total wrist arthrodesis, which fuses the radius, some of the carpal bones and one of the metacarpal bones. While these procedures alleviate pain and discomfort, they greatly restrict the range of motion of the wrist resulting in quality of life issues for the patient by limiting the utility of the wrist. In addition, in certain circumstances, because the bones in question are too deteriorated, or, in the case of fractures, not available, fusion is not possible.
In such circumstances, an available treatment is to replace all or some of the carpal bones with a prosthetic wrist in a procedure commonly referred to as a total wrist replacement. Although previous efforts have been made to develop prosthetic wrists, they have met often with disappointing results. Presently available wrist prostheses provide too limited a range of motion, dislocate too easily, place too much stress on bones resulting in failure or fractures, cause complications such as infections, and wear prematurely requiring additional surgeries during the patient's lifetime, among other flaws. In addition, the methods presently used for implanting such prosthetic wrists often result in poorly aligned joints and poor joint performance.
Accordingly, there is a need in the art for a prosthetic wrist, and associated methods for implanting same, which provides a patient with a range of motion that approximates that of a healthy wrist, is long-lasting, provides adequate support for the remaining hand and forearm bones, and avoids many of the drawbacks of existing prosthetic wrists.